1. Field of the Invention
The present invention relates to a plasma processing apparatus employing the RF induction method.
2. Description of the Related Art
In semiconductor wafer processing steps, dry etching is performed for, e.g., isolation of capacitors and elements and formation of contact holes. A parallel plate type plasma processing apparatus is known as a representative or conventional apparatuses that perform dry etching.
In this conventional apparatus, a rest table serving also as a lower electrode is disposed in an airtight chamber into which a process gas is supplied, and an upper electrode serving also as a gas supply section is disposed above the rest table to oppose it.
In this plasma processing apparatus, first, a wafer is placed on the rest table, and a process gas is supplied from the gas supply section. Simultaneously, an RF power is applied across the two electrodes by an RF power supply in order to generate a plasma, thereby etching the wafer by reactive ions in the plasma.
The line width of patterns of a device is more and more decreasing. When a plasma is generated in the above apparatus, the pressure in the chamber is 100 mTorr to 1 Torr. Under this high pressure, since the mean free time of ions is short, micropatterning is difficult to perform. Also, the diameters of wafers are increasing. When the mean free time of ions is short, a high uniformity of the plasma distribution over a wide surface cannot be ensured, and thus it is difficult to uniformly process a wafer having a large diameter.
For this reason, recently, employment of the RF induction method has been studied. According to this method, as described in European Pat. Appln. KOKAI Publication no. 379828 and Jpn. Pat. Appln. KOKAI Publication No. 3-79025, the upper wall portion of a chamber opposing a rest table is constituted by an insulating member, e.g., a quartz glass member, and a flat coil is mounted on the outer surface of the insulating member. An RF current is supplied to this coil to form an electromagnetic field in the chamber. The electrons flowing in the electromagnetic field are caused to collide against neutral particles in the process gas, thereby generating a plasma.
According to his method, a substantially concentric electric field is induced in accordance with the shape of the coil, thereby providing a plasma confining effect. When compared to the conventional parallel plate type plasma processing apparatus, the plasma can be generated with a comparatively low pressure. Accordingly, the mean free time of ions in the generated plasma is long,. Therefore, etching by means of this plasma is suitable for micropatterning. The plasma is diffused from a high-density area to a low-density area. Since the mean free time of ions is long, the plasma density distribution is smooth. Thus, the uniformity of the plasma on a plane parallel to the flat surface of the wafer is high, thereby increasing the uniformity within a plane of plasma processing for a wafer having a large diameter.
In this manner, an RF induction method attracts attention as a method suitable for micropatterning and processing of wafers with large diameters. However, to out the RF induction method into practical use, various problems must be solved. For example, one problem is as follows. Since the RF antenna is provided outside the chamber, if a large power is applied to the antenna, electromagnetic interference is caused around the antenna. Thus, the RF antenna must be covered with a shield, leading to a large-sized, complicated apparatus. When the upper wall of the chamber is made of quartz and the RF antenna is placed on the upper wall of the chamber, as the quartz has a small thermal conductivity, a portion of the chamber in contact with the antenna is locally heated upon application of power. Then, a large thermal stress is generated in quartz to cause cracking, leading to explosion of the chamber.